Metal nanoparticles having a particle diameter of 100 nm or less are utilized as the major component of electronic wire-forming material. For example, JP-A 2010-177084 (KOKAI) proposes a method of producing metal nanoparticles superior in dispersing stability on an industrial scale.
In recent years, a method has been developed in which ink containing metal nanoparticles is jetted directly on a base material by an ink jet method to form an intended wire pattern. In the ink used in the ink jet method, it is required to disperse metal nanoparticles stably. Also, a film obtained by sintering of nanoparticles when the written pattern is baked needs to have good conductivity.
Gold nanoparticles and silver nanoparticles each have a surface which is scarcely oxidized. Ink containing such particles is used to write a circuit pattern, followed by baking, thereby enabling the formation of a highly conductive film. However, these gold nanoparticles and silver nanoparticles are expensive.
Copper nanoparticles are more inexpensive than gold nanoparticles and silver nanoparticles and also have high resistance to electro-migration. However, copper nanoparticles have poor dispersing stability in a solvent, so that they easily form aggregates. Moreover, when copper nanoparticles are baked to obtain a conductive film, it is necessary to bake them at higher temperatures than temperatures in the case of gold nanoparticles and silver nanoparticles. Also, because copper nanoparticles each have an easily oxidizable surface, they are baked in a reducing gas atmosphere. Because the obtained conductive film is not free from volumetric shrinkage along with the reduction of oxidizing components, good conductivity is not obtained.